The polyester-polyether copolymer in which the aromatic polyester units constitute hard segments and the polyalkylene oxide units constitute soft segments has recently been in the spotlight as a new thermoplastic elastomer which will replace conventional natural rubbers and synthetic rubbers.
Having a comparatively low softening point and good flowability, such a polyester-polyether copolymer can be molded economically by conventional molding processes, such as extruding and injection molding, for thermoplastics. In addition, it has outstanding rubbery elasticity, good adhesion, and chemical resistance, and many other good properties. The polyester-polyether having these preferable properties is expected to find many uses such as in tubes, hoses, belts, tires, films, elastic fibers, and so on.
It is known that if an organotin compound is used alone or in combination with an organotitanium compound as a polycondensation catalyst in the production of the polyester-polyether copolymer, a copolymer having a high degree of polymerization and high whiteness can be obtained. (See Japanese Laid-Open Patents No. 52-6796 (1977) and No. 51-144489 (1976).) However, polyester-polyether copolymers are subject to severe deterioration due to oxidation decomposition when exposed to hot air, particularly air hotter than 120.degree. C., for a long time as described in U.S. Pat. Nos. 3896078. This tendency is also found in the polyester-polyether copolymer prepared by using an organotin compound as a polycondensation catalyst.
According to these U.S. Patents, the polyester-polyether copolymer is incorporated with an amide linkage-containing material and an antioxidant or an amide-containing phenolic antioxidant in order to improve the resistance to oxidation. When these compounds are incorporated, the resulting polyester-polyether copolymer is greatly improved in its resistance to oxidation, but is not necessarily satisfactory in performance for practical use. In other words, such a copolymer has poorer mechanical properties and exhibits discoloration on exposure to hot air.